Parameter - perimeter

These two words can be confused. Both are more used in technical and academic contexts than in everyday life. As they sound similar, although not identical, inexperienced students can be muddled between them - and the spell-checker can allow a typing mistake to incorporate the wrong one in your writing.

• Parameter has various technical meanings in subjects where maths is important.
  • In Mathematics itself, it is 'a [kind of] variable', and in Geometry a specific measurement of a conic section.
  • In Astronomy, it is one of the 'elements' whose measurement can describe the orbit of a heavenly body.
  • Other such very restricted - and very precise - meanings for crystallography, electronics and statistics are recorded in OED.
• In more ordinary usage, a parameter is one of the characteristics, usually measurable, by which something can be defined. In Music, for example, a note can be described by reference to several parameters such as pitch, length and volume. Parameters can also be the limits, or boundaries, of something: in computing, a repeated routine may be performed within the parameters 'for a = 0 to 100'.

It is this last usage that may most often lead to confusion with perimeter.

• Perimeter is derived from the Greek meaning 'measurement around'. Originally, in Geometry, it meant the continuous line which forms the boundary of a closed figure, or the length of such a line. The circumference of a circle is the best-known example of a perimeter. Various figurative and extended meanings follow. Notably, military and security personnel commonly defend the perimeter of a position: a more or less continuous 'line', either imaginary or marked by walls, wire fences and so on. The wire fences that surround sensitive places such as military bases, airfields and prisons to prevent entry by hostile persons are known as perimeter fences.

If your tutors complain about a confusion that you make of these two words, you may be encouraged to know that you are in good company. OED (2nd edition, 1989) notes, s.v. parameter, [Etymology], that "Non-technical uses of parameter have attracted adverse comment from usage guides in the later 20th cent., particularly as inaccurate applications of the mathematical and computing use to general situations, and through association or confusion with perimeter; see, for example, Sir Bruce Fraser's revision of Sir Ernest Gowers's Compl[ete] Plain Words (1973) 79.